Wires that are used in applications that involve exposure to high temperatures are typically coated with relatively expensive polymers, such as fluoropolymers or polyether ether ketone (PEEK). Less expensive polymers normally fail to provide the combination of physical properties, chemical resistance, and thermal resistance that are demanded in such applications. For instance, polyphenylene sulfide (PPS), a specific type of polyarylene sulfides, possesses many of the needed characteristics for utilization in coating wires, but has a maximum continuous use temperature (CUT) of only about 170° C. More specifically, PPS offers excellent solvent, chemical, and heat resistance. It also possesses high strength, stiffness and low elongation at yield and break. However, PPS cannot be used in coating wires that are utilized in applications involving exposure to high temperatures without compromising the maximum continuous use temperature of the wire.
U.S. Pat. No. 6,608,136 discloses a polyphenylene sulfide alloy composition for wire and cables that comprises 40 to 90% by weight of PPS, about 1 to about 20% of an ethylene based grafting agent with grafting groups selected from unsaturated epoxide, unsaturated isocyanate, silane, or an oxazoline, and another ethylene copolymer with carboxylic acid containing groups. However, such compositions do not provide adequate high temperature resistance for utilization in many wire coating applications.
U.S. Pat. No. 4,421,588 discloses a plastics alloy for a bearing material comprising polyphenylene sulphide and polyether ether ketone. The alloy is formed by powder mixing, melt blending or solvent blending and applied to a metal backing either as a sheet, or in solution or in powder form. The alloy is heated and roll bonded to the backing.
U.S. Pat. No. 4,684,699 discloses an alloy comprising from about 2 to about 98 weight percent of a poly(arylene sulfide) and from about 98 to about 2 weight percent of a crystalline poly(aryl ether ketone).
U.S. Pat. No. 4,690,972 discloses compositions comprising a poly(arylene sulfide) which crystallizes to a fine-grained crystalline morphology. A method is also provided for treating compositions comprising a poly(arylene sulfide) by incorporation of a crystalline morphology altering additive, heating the resulting mixture above the melting point of the poly(arylene sulfide) and cooling the mixture at a rate of less than 50° C. per minute.
U.S. Pat. No. 5,095,078 discloses a heat-resistant film obtained by biaxially-stretching a composition which comprises (A) 50-90 parts by weight of a polyether ether ketone having predominant recurring units of the formula:
and (B) 50-10 parts by weight of a substantially linear poly(arylene sulfide) having melt viscosity of at least 1,000 poises. A production process of such a heat-resistant film is also disclosed, which comprises biaxially stretching the above composition in a temperature range at least equal to the crystallization temperature (Tc) of the poly(arylene sulfide) but not higher than the crystallization temperature (Tc) of the polyether ether ketone.
U.S. Pat. No. 5,223,585 discloses a heat-resistant film obtained by biaxially-stretching a composition which comprises (A) 50-90 parts by weight of a polyether ether ketone having predominant recurring units of the formula:
and (B) 50-10 parts by weight of a substantially linear poly(arylene sulfide) having melt viscosity of at least 1,000 poises.
U.S. Pat. No. 5,286,814 discloses a heat-resistant stretched film that is obtained by stretching a resin composition comprising 100 parts by weight of a poly(arylene sulfide) of a substantially linear structure and 5 to less than 100 parts by weight of a melt-stable poly(arylene thioether-ketone).
U.S. Pat. No. 5,079,290 describes a blend of polyarylene sulfide and polyetherether ketone at a low level up to 3% by weight for increased nucleation. The patent does not suggest that the upper use temperature of polyarylene sulfide can be increased by this small addition of polyarylene ether ketone.
U.S. Pat. No. 4,935,473 describes a composition comprising 100 parts of polyphenylene sulfide and a small amount of another thermoplastic polymer that includes a polyarylether ketone. The patent does not teach that the upper use temperature can be increased by higher PEEK additions and by using a PPS of higher sodium end group concentration.
U.S. Pat. No. 5,256,715 describes a polyarylene sulfide composition containing one azidosilane compound and an optional nucleating agent. Unfortunately, the levels required for nucleation are small and do not suggest the increase the continuous use temperature of the polyarylene sulfide.
U.S. Pat. No. 5,300,552 describes a polyarylene sulfide composition with a polyether ether ketone included as a nucleating agent at levels of up to 2% by weight. At these low amounts of polyether ether ketone (PEEK), an increase in the upper use temperature of the polyarylene sulfide is not possible.
U.S. Pat. No. 5,352,768 describes a process for producing polyarylene sulfide polymer. Addition of PEEK at less than 1% is suggested for facilitating nucleation which is considered ineffective in increasing the upper use temperature of PPS and improving the tensile strength of the blend of polyarylene sulfide and polyether ether ketone.
There is currently a need for a less expensive polymer composition for coating wires that are used in applications that involve exposure to high temperatures for extended periods of time. Such a composition should possess good tensile properties, modulus, chemical resistance, and flexibility in addition to good thermal characteristics, as exemplified by a high continuous use temperature. It would be particularly desirable to utilize poly-aryl-ether-ketone in amounts that are high enough to improve the continuous use temperature, yet not high enough to increase the cost appreciably. It is also important for such a polymeric composition to be capable of being processed using standard wire coating procedures and equipment.